Intracellular pH (pHi) alterations by metabolic or respiratory acidosis/alkalosis and/or hypoxia has been associated with physiological function and pharmacological intervention. Changes in pHi will be seen with newly developed pH-microelectrodes inserted directly into cardiac cells of guinea pigs. Experimental conditions mimicking the above indicated pathological states will be induced and direct measurements of changes in pHi will be made of not only the resting state (resting potential) but also effects occurring during generation of action potentials. It is anticipated that the kinetics associated with pHi and tissue function (physiological and biochemical) will be elaborated. Additional data will be forthcoming upon installation of other newly developed intracellular ion/enzyme electrode sensors.